Cellular immunolocalization of occludin during embryonic and postnatal development of the mouse testis and epididymis

Cellular junctions in the testis and epididymis play crucial roles for the development and maturation of spermatozoa. In the testis, tight junctions b etween Sertoli cells form a functional blood testis barrier between 10 and 16 days of age, whereas the tight junctional blood epididymal barrier betwe en adjacent epithelial cells is formed between days 18 and 21. In the prese nt study, occludin, a constituent integral membrane protein of tight juncti ons, was localized by immunofluorescent confocal microscopy in embryonic(da ys 13.5-18.5), postnatal (days 5-23) and adult (day 70) mouse testes and ep ididymides to correlate its expression with the onset of tight junctions an d eventual formation of these barriers. At embryonic days 13.5 and 16.5, lo w diffuse cytoplasmic levels of occludin were observed in cells of the test icular cords. By embryonic day 18.5, the level of occludin was still low bu t appeared as a filiform-like network streaming toward the center of the co rd. At postnatal days 5 and 7 immunostaining became more intense and appear ed to outline the periphery of Sertoli cells of seminiferous tubules. Postn atal day 14 marked the appearance of an intense, focal band-like localizati on of occludin at the base of the tubules, correlating with the appearance of a functional blood-testis barrier. By day 23 and in adults, expression o f occludin was noted at the base of the tubule appearing as intense, wavy, discontinuous bands similar in appearance irrespective of the stage of the seminiferous epithelium cycle. In the developing epididymis, intense cytopl asmic immunostaining was present in epithelial cells of many epididymal tub ules at embryonic day 13.5. By embryonic day 16.5, intense occludin immunos taining appeared along the lateral plasma membranes of epithelial cells, wh ereas at embryonic day 18.5, immunostaining was punctate and apically locat ed, suggesting the presence of tight junctions by this age; similar immunos taining was noted at postnatal days 5 and 7. In the adult epididymis, disti nct punctate apical staining was observed between adjacent principal cells of all epididymal regions except the proximal initial segment, where occlud in was found only in association with narrow cells. These results indicate that in the epididymis, the appearance of occludin at epical sites between adjacent epithelial cells occurs during embryonic development suggesting th at tight junctions form earlier than in the testis. While occludin was expr essed in a similar pattern between Sertoli cells at all stages of the cycle in the adult testis, its expression in the adult epididymis was cell- and region-specific. Taken together these data suggest that different factors r egulate occludin expression in the testis and epididymis.